The present invention relates to a novel improvement of a thermal analyzing apparatus for examining change in temperature or time of a material physical property. More specifically, the invention relates to a novel improvement of a furnace tube structure of a thermal analyzing apparatus for measuring an evolved gas from a sample on a thermal analyzing apparatus by a Fourier transform infrared spectroscopic photometer.
Conventionally, an approach has been frequently practiced that an evolved gas from a sample within a thermal analyzing apparatus is analyzed by another gas analyzing apparatus. The thermal analyzing apparatuses for conducting this approach, in particular, often use a thermogravimetric measuring apparatus (hereinafter abbreviated as TG) while the evolved gas analyzing apparatuses often use a Fourier transform infrared spectroscopic photometer (hereinafter abbreviated as FT-IR), mass spectrometric apparatus, gas cromatograph mass spectrometric apparatus, etc. Among them, as a method for measuring an evolved gas from a sample within TG by FT-IR there is an apparatus having a structure, for example, as shown by R. Kinoshita et al., J. Thermal Anal., 38(1992)1891-1900. In this apparatus, an evolved gas from a sample within TG is introduced into a gas cell through a transfer line attached to a tip of a furnace tube. The IR light from FT-IR is incident through a window of the gas cell so that IR absorption is made due to the evolved gas introduced in the gas cell when IR light is passing trough the gas cell and IR absorption is detected by a downstream detector. The furnace tube, the transfer line and the gas cell are held in temperature for a purpose of prevention against condensation of the evolved gas. The heat insulation, in general, often uses 200.degree. C.-300.degree. C. The gas cell has a detailed structure, as shown by David A. C. Compton, David. J. Johnson, Research & Development, February (1989), having a heat insulation heater around a cylindrical metal tube and an IR transmissive window member (ZnSe and KBr) in a cylindrical opening. The evolved gas from the TG is introduced from a cylindrical metal tube side face through a transfer line, and discharged from a separately-provided discharge port. The IR light is incident from one opening of the metal tube through a window member, and outgoing through the window member in the other opening, being guided to a detector.
Also, in Nicolet FT-IR Technical Note TN-8714, there are shown a gas cell 46 with a structure as was shown in FIG. 4 and an interface to a TG furnace tube. The gas cell 46 is cylindrical and sealed at one opening by a reflection mirror 43 and at the other by a window member 42 transmissive of IR light so that an evolved gas from TG is introduced from a cylindrical gas cell 46 side face through an inlet line 44, and discharged through a gas discharge line 45 provided in the gas cell side face. The gas inlet line 44 is made of glass and connected to a top of a furnace tube by a glass ball joint. The gas cell main body is accommodated in a heat-insulated chamber 41 and held at a temperature of up to 325.degree. C. as maximum.
There is real time property as one important point in TG/FT-IR measurement. That is, in order for a point that the evolved gas from a sample within TG is to be detected on an IR side with a time lag as low as possible, there is a necessity to introduce the evolved gas in TG into the gas cell as soon as possible. The methods for improving real time property include a method of reducing as low as possible a capacitance of a connection means from the TG side to the gas cell thereby decreasing a dead volume, and a method of increasing a flow rate of carrier gas to introduce as early as possible to the gas cell. However, the increase in flow rate of carrier gas results in decrease in concentration of the evolved gas within the gas cell, wherein decrease in absorption sensitivity is observed and hence excessive increase is not desired. Accordingly, generally taken is a method of reducing a dead volume as low as possible in the connection means. Because the conventional examples in either case is to reduce a dead volume in the connection means as low as possible, the TG furnace tube and gas cell are connected using a thin tubular connection means such as a transfer line, inlet line or the like. Also, furthermore, heat insulation is conducted in both the connection means and the gas cell for the purpose of preventing against gas condensation.
However, the thin tubular connection means is comparatively difficult to evenly keep temperature and liable to form temperature distribution. Accordingly, there is a case that a cold spot is formed that is lower than an objective heat insulation as the case may be. In particular, the connection part with the furnace tube or gas cell connects between different formed parts and hence difficult to conduct heat insulation, readily turned to a cold spot. In some measurements there are cases a gas with a high boiling point is evolved to be possibly condensed at a cold spot. There is a defect that, once condensation occurs, the flow passage is narrowed and hence evolved-gas blockage becomes more ready to occur finally blocking the flow passage completely.
Although in order to prevent condensation of an evolved gas with a high boiling point there is a method of heat insulation at a higher temperature, in conventional examples a maximum temperature is around 325.degree. C. at the most. Because the conventional example transfers the gas using a thin tubular connection means, enclosure property is required to a gas cell discharge port and seal members are used also in the window portions of the connection part and gas cell. However, the raise of temperature causes a problem of heat resistance of the seal member and a problem of weakening sealability, having a defect of not suited for heat insulation at excessively high temperature.
Recently, in analyzing dust-incineration evolved gases from incinerators there is a desire of identifying substances that are not in a gaseous state unless at a high temperature close to 500.degree. C. However, in the conventional example TG/FT-IR system there is a defect that heat insulation is difficult at 500.degree. C. and hence nothing is coped with.
It is a problem of the present invention to provide a thermal analyzing apparatus which is capable of insulating heat at a high temperature of 500.degree. C. and higher without spoiling real-time property and free from blockage in flow path due to condensation of an evolved gas.